1. Coolant Level and System Integrity:
* Low Coolant: Check your coolant level in the radiator and overflow reservoir. If it's low, you have a leak somewhere in the cooling system. Low coolant means the heater core isn't getting enough hot coolant to heat the air. Top it off (with the correct 50/50 mix of coolant and distilled water) only if you're certain there's no leak; otherwise, you'll just keep losing coolant.
* Leaks: Look for signs of leaks around the radiator, hoses, water pump, and heater core itself (this is harder to see directly). Look for stains, puddles, or dampness. A pressure test by a mechanic might be necessary to pinpoint a leak.
* Thermostat: A stuck closed thermostat prevents coolant from circulating properly, including to the heater core. A failing thermostat may also open and close erratically, causing inconsistent heating.
2. Heater Core Issues:
* Clogged Heater Core: Over time, the heater core can become clogged with debris, restricting coolant flow. This reduces heating efficiency or stops it altogether. This often requires replacement.
* Heater Core Leak: A leak in the heater core can lead to coolant loss (potentially without external evidence) and, of course, no heat. This often manifests as a musty smell in the car, especially after the heater has been running for a while (the smell is the coolant leaking and evaporating). Repair usually involves replacing the heater core, a job that often requires partial dashboard disassembly.
3. Blower Motor and Controls:
* Blower Motor: Check if the fan is actually blowing air. If not, the problem might be with the blower motor itself, its resistor (which controls fan speed), or the blower motor fuse/circuit breaker. Test the fan on all speeds.
* Blend Door Actuator: This is a small motor that controls the mix of hot and cold air. If it's malfunctioning, it may be stuck on cold air, even if the heater core is hot. This is a more involved repair.
* Control Panel: A faulty control panel could also prevent warm air from being directed to the vents. This is less common than the other issues.
4. Other Considerations:
* Air in the System: Air trapped in the cooling system can prevent proper circulation of coolant. "Burping" the system (carefully releasing trapped air) might help, but this is usually best done by a mechanic.
Troubleshooting Steps:
1. Check coolant level.
2. Inspect for leaks visually.
3. Check the thermostat (feel the upper radiator hose – it should be hot when the engine is at operating temperature).
4. Test the blower motor on all speeds.
5. Feel the heater core hoses (if accessible) – both should be hot when the heater is on.
If you're not comfortable with any of these steps, take your Buick to a qualified mechanic for diagnosis and repair. Many of these problems, particularly heater core issues, are difficult to diagnose and fix without experience. Trying to fix a leaking heater core yourself could lead to further damage, especially on an older car like a 1990 Buick Regal.
